The present invention concerns a process for monitoring the movement of a motorized door, including an electrical system for carrying out the process. Power operated doors and gates must be monitored by associated electrical systems to prevent them from causing damage to objects or injuries to persons which unintentionally come into the path of the motion of the door while it is being operated. In the past, various devices have already been developed that offer such protection against obstacles in the door's path. Presently, electrical sensors or the like are arranged under elastic strips along the edge of a given door or gate which forms electric contacts which switch off the drive or reverse the direction of movement of the door when the switch is tripped. Such sensors, of which the sensitivity may be a function of the their design, can be arranged anywhere along the door or gate being driven. However, such switches are ineffective when an obstacle such as a car or other vehicle runs into the door being closed outside the edge or location in which such switches are located.
Other systems presently used measure the delay of the door, being driven by a power transmission, by detecting or otherwise sensing an increase in the loading of a driving chain or driving transmission of some sort. Generally, these systems are designed such that any increase in the driving force, than normally necessary to move the door, will cause a switching action such as to reverse or stop the door.
All the above described monitoring systems and devices are based on the fact that a certain force is necessary for the normal, unobstructed movement of a door or gate. The driving force necessary is monitored to see whether it exceeds a certain, preset difference value. This threshold value or difference value would understandably be the greatest force which would be encountered in the normal operation of the door or gate.
The force necessary for the movement of a door or gate, particularly an overhead door being raised along a track in an upright position as disclosed in the later drawings, is not constant over the entire path of operation. This inconsistency can be due to the construction of the door, and it occurs when wind effects and other local conditions of operation are also taken into account. Different weight relations and friction effects occur in many doors because of the displacement of the door leaf, but can be compensated for only after great expense. Such compensation is quite difficult under most practical operating conditions and environments. An example of these difficulties can be observed in the case where the door weight being driven along a track is compensated for by springs which may exert a differing force when wear occurs or there are different operating temperatures, or other types of damage which can be observed in industrial use. Consequently, the value of the drive force required to move a door in question, such as that disclosed in the present invention, is dependent on the tracks provided for the movement of said door, or what can be described as the transfer path. The maximum value of the force required has been used in the past as the criterion for the setting of threshold limits for switching off the drive motor.